The invention process is concerned with the enhanced recovery of oil from underground formations. More particularly, the invention relates to the length of horizontal production wells located between vertical production wells in patterns containing horizontal and vertical wells.
Horizontal wells have been investigated and tested for oil recovery for quite some time. Although horizontal wells may in the future be proven economically successful to recover light petroleum from many types of formations, at present, the use of horizontal wells is usually limited to formations containing highly viscous crude. It seems likely that horizontal wells will soon become a chief method of producing tar sand formations and other highly viscous oils which cannot be efficiently produced by conventional methods because of their high viscosity.
Various proposals have been set forth for petroleum recovery with horizontal well schemes. Most have involved steam injection or in situ combustion with horizontal wells serving as both injection wells and producing wells. Steam and combustion processes have been employed to heat viscous formations to lower the viscosity of the petroleum as well as to provide the driving force to push the hydrocarbons toward a well.
U.S. Pat. No. 4,283,088 illustrates the use of a system of radial horizontal wells, optionally in conjunction with an inverted 9-spot having an unsually large number of injection wells. U.S. Pat. No. 4,390,067 illustrates a scheme of using horizontal and vertical wells together to form a pentagonal shaped pattern which is labeled a "5-spot" in the patent, although the art recognizes a different pattern as constituting a 5-spot.